I should to reproduce this behavior

I've tried using NSGradient with a simple linear gradient in order to fill it but it's a poor result. What kind of gradient is it?
I should to reproduce this behavior

I've tried using NSGradient with a simple linear gradient in order to fill it but it's a poor result. What kind of gradient is it?
Are you putting the button in a UINavigationBar or a toolbar?
UIBarButtonItem will do that shading on its own, but it tends to live in a toolbar or navbar.